Tie-down compensation for an elevator system

ABSTRACT

An elevator system ( 20 ) includes a tie-down compensation arrangement ( 40 ). A tension member ( 42 ) extends between a cab ( 22 ) and counterweight ( 26 ) to provide a desired amount of tension on a load bearing rope or belt ( 30 ) that supports the cab and the counterweight. The tension member ( 42 ) in one example comprises a coated steel belt. At least one sheave ( 46 ) is supported on a base module ( 48 ) and remains stationary relative to a floor of a pit ( 52 ). A damper ( 50 ) is supported for movement with the counterweight ( 26 ) or the cab ( 22 ) to absorb energy that would otherwise tend to cause counterweight jump following a rapid descent and stop of the cab ( 22 ).

FIELD OF THE INVENTION

This invention generally relates to elevator systems. More particularly,this invention relates to a unique arrangement for maintaining tractionand control within an elevator system.

DESCRIPTION OF THE RELATED ART

There are a variety of modern elevator systems. One common arrangementincludes a cab and a counterweight suspended by a rope or belt. Amachine causes the rope or belt to move along at least one sheave tocause a desired movement of the cab between landings within a hoistway,for example. In a typical arrangement, as the cab moves up, thecounterweight moves down and vise versa.

The weight associated with the counterweight and cab typically causetension on the rope or belt sufficient to maintain traction between thebelt and the sheave that causes the desired elevator cab movement. Thereare situations, however, where tie-down compensation is desirable tomaintain adequate rope traction. Lightweight cars and counterweights,while having other advantages, are more susceptible to the effects ofshifting rope weight as the car moves through the hoistway, which canreduce traction.

Tie-down compensation arrangements limit potential “counterweight jump,”which may otherwise occur as the cab moves rapidly downward and thenstops. Under such circumstances the inertia associated with the upwardmovement of the counterweight can cause the counterweight to continuemoving upward even though the cab has stopped moving downward. Suchupward movement of the counterweight introduces slack into the ropeuntil the counterweight subsequently falls to the point where the ropeis again under tension. Such counterweight jump is undesirable forobvious reasons.

Typical compensation arrangements include chains, free rope and thesystems having a large, moveable mass in the hoistway pit, each of whichcan provide tension for certain elevator system designs. While sucharrangements have been useful, they are not without shortcomings anddrawbacks. The significant drawback associated with conventionaltie-down compensation arrangements is that they require a relativelylarge pit depth at the bottom of a hoistway. Modern building practicesand associated economies favor shallower pit depth. In some instances,the depth required to use a conventional tie-down compensationarrangement exceeds that which is available. In some circumstances, theoption of not using tie-down compensation is chosen if it is notrequired by a corresponding code, for example. Without suchcompensation, however, there is an increased likelihood thatcounterweight jump will occur.

Higher rise buildings further complicate the situation. For example,buildings that have a rise above 400 feet typically are not compatiblewith a chain compensation arrangement. However, the available pit depthoften does not accommodate a free rope or moveable mass-basedcompensation arrangement. Using chain or free-rope compensationarrangements in such buildings can leave open the possibility forcounterweight jump.

There is a need for an improved tensioning assembly that ensuresappropriate traction for moving the elevator cab and minimizes or avoidscounterweight jump. This invention addresses that need while avoidingthe shortcomings and drawbacks of previous systems. The inventivearrangement is capable of fitting within a much smaller pit compared tothe pit depth required for the previous approaches.

SUMMARY OF THE INVENTION

In general terms, this invention is an assembly that maintainsappropriate tension on a load bearing rope or belt within an elevatorsystem and minimizes the possibility for counterweight jump.

One example system designed according to this invention includes anelevator cab and a counterweight. A load bearing member is associatedwith the cab and counterweight. A tension member extends between the caband the counterweight. A base module has at least one sheave thatrotates about an axis that remains fixed beneath the lowest position ofthe cab. The tension member at least partially wraps around the sheave.

Another example system includes a damper supported for movement with thecab or the counterweight. The damper absorbs energy that otherwise wouldcause counterweight jump.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates selected portions of an elevator systemincluding a tie-down compensation arrangement designed according to anembodiment of this invention.

FIG. 2 a schematically illustrates an embodiment designed according tothe embodiment of FIG. 1 and is a view taken along the lines 2-2 in FIG.1.

FIG. 2 b schematically illustrates an alternative embodiment designedaccording to the embodiment of FIG. 1 and is a view taken along thelines 2-2 in FIG. 1.

FIG. 2 c schematically illustrates another alternative embodimentdesigned according to the embodiment of FIG. 1 and is a view taken alongthe lines 2-2 in FIG. 1.

FIG. 3 schematically illustrates an alternative embodiment as that wouldbe seen taken along the lines 3-3 in FIG. 1.

FIG. 4 is a perspective, diagrammatic illustration of an example basemodule designed according to an embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows an elevator system 20 including a cab 22 thatis supported by a frame 24 in a conventional manner. A counterweight 26has an associated frame 28. A load bearing member 30, such as a rope orbelt, supports the weight of the cab 22 and the counterweight 26 in aconventional manner. A conventional hitch arrangement 32 secures anappropriate portion of the load bearing member 30 to the cab frame 24.Similarly, a conventional hitch arrangement 34 secures an appropriateportion of the load bearing member 30 to the counterweight frame 28. Amachine (not illustrated) includes at least one drive sheave that causesmovement of the load bearing member 30 and corresponding movement of thecab and counterweight within a hoistway 36 to move the cab 22 betweenlandings in a building, for example.

The illustrated example includes a tension and compensation arrangement40. An elongated tension member 42 extends between the cab 22 and thecounterweight 26. In one example, the tension member 42 comprises atleast one steel-core, rubber coated belt. In one example, the belt has awidth of 30 mm and is 9.4 mm thick. This example tension member 42 issignificantly different than a rope or chain used in conventionalcompensating arrangements. As can be appreciated from FIG. 2 a forexample, the tension member 42 preferably comprises a plurality ofbelts. The illustrated example of FIG. 2 a includes a total of six suchbelts.

One end of the tension member 42 in this example is secured to aselected portion of the cab frame 24 using a termination 44. In oneexample, the termination 44 comprises a taluret style ending secured toa selected plank of the cab frame 24. A variety of terminations tosecure the tension member to the cab frame 24 may be used. Those skilledin the art who have the benefit of this description will be able toselect a termination arrangement that meets their particular needs. Thetension member 42 at least partially wraps around sheaves 46 that arepart of a base module 48. In the example embodiment of FIG. 1, the otherend of the tension member 42 is secured to a damper 50 that is supportedfor movement with the counterweight through the hoistway 36. The sheaves46 and the base module 48 remain in the pit 52 such that the sheave axesof rotation do not move relative to the bottom surface of the pit 52.

In one example, the sheaves 46 are made from plastic and are grooved toaccommodate the desired number and configuration of the belts used forthe tension member 42. In one example, the sheaves 46 are 178 mm wideand each accommodates three tension member belts. In this example, thesheaves have a diameter of 320 mm. An advantage to using such a sheaveis that it is relatively lightweight and provides design flexibility incustomizing the groove designs on the sheave.

The tension member 42 extending beneath (according to the drawings) thecab 22 and counterweight 26 insures that appropriate tension remains onthe load bearing member 30 to provide the desired traction within theelevator system. Further, the arrangement 40 minimizes the possibilityfor counterweight jump and, in most circumstances, eliminatescounterweight jump.

The illustrated example also includes a cab damper 54 and acounterweight damper 56, which are schematically shown and operate in aconventional manner.

Referring now to FIG. 2 a, the damper 50 of one example embodiment isschematically shown. The counterweight 26 includes a conventional strikeblock 58 that cooperates with the damper 56 in a known manner. Thedamper 50 is supported for movement with the counterweight 26 and, inthis example, includes air springs 60 that operate to dampen anymovement of the counterweight 26 that would correspond to acounterweight jump. The air springs 60 absorb energy that wouldotherwise cause the counterweight 26 to rise in a counterweight jumpmovement.

The air springs 60 are supported between a stationary plank 62 and amoveable plank 64. The plank 62 remains fixed relative to thecounterweight frame 28. The plank 64 is slidable within grooves 66formed on vertical members 68 of the counterweight frame 28. In oneexample, the grooves 66 and the air springs 60 accommodate a maximumstroke or movement of 5.7 inches. In one example, the air springs 60have a load range between 1,600 and 2,500 pounds with a maximum capacityof 2,750.

The tension member belts 42 include terminations 70 that are secured tothimble rods 72. Springs 74 are associated with opposite ends of thethimble rods 72 and are received against a side of the plank 64 oppositefrom the air springs 60. The springs 74 bias the ends of the thimblerods away from the plank 64. The ends of the thimble rods 72 and thesprings 74 in this example are received in a space between the plank 64and the stationary plank 76, which provides a support for the fillers 78provided to achieve the desired mass of the counterweight 26.

During normal elevator operation, the tension member 42 is kept undertension, in part, by the bias of the springs 74. One function of thesprings 74 is to accommodate any belt stretch in the tension member 42during the service life of the elevator system.

Under some circumstances, such as when the cab 22 moves downwardrelatively quickly then stops, the springs 74 dampen an initial tendencyof the counterweight 26 to continue moving upward even though the cab 22has stopped moving downward. Once the bias of the springs 74 is overcomeand the springs 74 are compressed a desired amount, the air springs 60are compressed allowing the plank 64 to move downward (according to thedrawing) toward the plank 62. Depending on a particular elevator systemconfiguration, those skilled in the art who have the benefit of thisdescription will be able to select appropriate springs 74 andappropriate air springs 60 to achieve the desired damping effect to meetthe needs of their particular situation. The compression of the springs74 followed by the compression of the air springs 60 operates to absorbthe energy that otherwise would tend to cause counterweight jump. Theair springs 60 also absorb the additional load on the tension member 42under such circumstances.

FIG. 2 b shows another example embodiment where pressurized actuators 80are supported between the moveable plank 64 and the stationary plank 62in place of the air springs 60 of the embodiment of FIG. 2 a. Thepressurized actuators 80 may be hydraulic or pneumatic devices forexample. In one example, the pressurized actuators 80 are loadsuppressors that are calibrated to drop or be compressed at a designedpoundage after the springs 74 have reached a desired maximum compressionand capacity. In one example, the actuators 80 are non-returning suchthat once they are compressed they do not return to the non-compressedstate (shown in FIG. 2 b, for example) without some manual adjustmentmade by a technician, for example. In another example, the actuators 80are switch released to return to a non-compressed state. In stillanother example, the actuators 80 are slow return load cells thatautomatically, slowly return to a non-compressed state where the plank64 is at the furthest possible distance from the plank 62.

The actuators 80 operate in the same manner as the air springs 60 inthat they compress to absorb the energy that otherwise would causecounterweight jump under appropriate circumstances.

FIG. 2 c shows another example embodiment where the damper 50 includesmechanical springs 82 in place of the air springs 60 or the actuators 80from the two previous examples. The mechanical springs 82 operate in thesame general manner to dampen movement of the counterweight relative tothe cab after the cab is stopped following a downward travel.

Although the three previous examples each include the damper 50supported on the counterweight frame 28, this invention also includes adamper 50 associated with the cab 22. FIG. 3 schematically illustratesan example arrangement where the damper 50′ is supported for movementwith the cab 22 rather than with the counterweight 26. In this example,air springs 84 similar to the air springs 60 of FIG. 2 a are associatedwith thimble rods and springs, which are associated with appropriateportions of the cab frame 24. The damper 50′ in this example performsthe same general function as the damper described in the previousexamples. Any movement of the counterweight 26 after the cab 22 hasstopped will be suppressed or damped by operation of the damper 50′.Similarly, any potential cab jump is controlled.

While the example of FIG. 3 shows air springs 84, it is possible toinclude pressurized actuators or mechanical springs similar to thoseused in the examples of FIGS. 2 b and 2 c as part of a damper supportedfor movement with the cab

The tension member 42 at least partially wraps around the sheaves 46,which are part of the base module 48 that remains stationary within thepit 52. FIG. 4 diagrammatically illustrates an example base modulearrangement. In this example, base supports 90 are secured to the floorof the pit 52 in a conventional manner. In one example, the basesupports 90 comprise steel I beams. Sheave supports 92 are secured tothe base supports 90 using conventional welding techniques or bolts, forexample. In this example, the sheave supports 92 and 94 compriseC-shaped steel beams. Axles 96 are supported by the sheave supports andallow the sheaves 46 to rotate freely responsive to movement of thetension member 42, which is responsive to movement of the cab andcounterweight within the hoistway as caused by movement of the loadbearing member 30.

A significant advantage to a tie-down compensation arrangement designedaccording to this invention is that it allows for a smaller pit depthyet still provides maximum functionality for maintaining a desiredtension on the load bearing member 30 and minimizing the likelihood forcounterweight jump. In one example, the inventive arrangement allows forusing a pit depth as shallow as 6′10½″ compared to conventionalarrangements that would require a pit depth of greater than 10′. In oneexample, a pit depth savings of almost 4′ is achieved using theinventive arrangement. This provides the significant advantage of beingable to use a tie-down compensation arrangement even for relatively highrise elevator systems where conventional chain compensation does notadequately address the tension and counterweight jump eliminationrequirements.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this invention. The scope of legal protection given tothis invention can only be determined by studying the following claims.

1. An elevator system, comprising: a cab; a counterweight; a loadbearing member extending between the cab and the counterweight so thatthe cab and counterweight move simultaneously; a tension memberextending between the cab and the counterweight, the tension memberproviding a desired tension on the load bearing member; and a dampersupported for movement with one of the cab or the counterweight, one endof the tension member being associated with the damper such that thedamper reduces motion of the cab or the counterweight when the other ofthe cab or the counterweight has stopped.
 2. The system of claim 1,including a stationary base supported beneath a lowest availableposition of the cab and a plurality of sheaves rotatably supported onthe base, the tension member moving along the sheaves as the cab andcounterweight move.
 3. The system of claim 1, wherein the sheavescomprise plastic.
 4. The system of claim 3, wherein the tension memberhas an outside dimension and the sheaves have a diameter that isapproximately thirty times greater than the tension member outsidedimension.
 5. The system of claim 3, wherein the sheaves have a diameterin the range from about 290 mm to about 330 mm.
 6. The system of claim1, wherein the tension member comprises a plurality of belts each havinga thickness of approximately 10 mm and a width of approximately 30 mm.7. The system of claim 1, wherein the damper comprises at least one ofan air spring, a pneumatic damper, a hydraulic damper or a mechanicalspring.
 8. The system of claim 7, including a first member actingagainst one side of the damper and a second member associated with anopposite side of the damper, the first member remaining stationaryrelative to the cab or counterweight with which the damper moves, thesecond member being moveable relative to the first member, the damperresisting movement of the second member toward the first member.
 9. Thesystem of claim 1, wherein the one end of the tension member is securedto at least one termination that is secured near one end of each of aplurality of thimble rods, an opposite end of the thimble rods beingpositioned on an opposite side of the second member from the damper andincluding a spring associated with each opposite end of each thimble rodto urge the opposite ends away from the second member.
 10. An elevatorsystem, comprising: a cab; a counterweight; a load bearing memberextending between the cab and the counterweight so that the cab andcounterweight move simultaneously; a tension member extending betweenthe cab and the counterweight, the tension member facilitatingmaintaining a desired tension on the load bearing member; and astationary base beneath a lowest available position of the cab and aplurality of sheaves rotatably supported on the base, the sheaves havingaxes that remain stationary, the tension member moving along the sheavesas the cab and counterweight move.
 11. The system of claim 10, includinga damper supported for movement with one of the cab or thecounterweight, one end of the tension member being associated with thedamper such that the damper reduces motion of the cab or thecounterweight when the other of the cab or the counterweight hasstopped.
 12. The system of claim 11, wherein the damper comprises atleast one of an air spring, a pneumatic damper, a hydraulic damper or amechanical spring.
 13. The system of claim 11, including a first memberacting against one side of the damper and a second member associatedwith an opposite side of the damper, the first member remainingstationary relative to the cab or counterweight with which the dampermoves, the second member being moveable relative to the first member,the damper resisting movement of the second member toward the firstmember.
 14. The system of claim 13, wherein the one end of the tensionmember is secured to at least one termination that is secured near oneend of each of a plurality of thimble rods, an opposite end of thethimble rods being positioned on an opposite side of the second memberfrom the damper and including a spring associated with each opposite endof each thimble rod to urge the opposite ends away from the secondmember.
 15. The system of claim 11, wherein the tension member has anoutside dimension and the sheaves have a diameter that is approximatelythirty times greater than the tension member outside dimension.
 16. Thesystem of claim 15, wherein the sheaves have a diameter in the rangefrom about 290 mm to about 330 mm.
 17. The system of claim 10, whereinthe tension member comprises a plurality of belts each having athickness of approximately 10 mm and a width of approximately 30 mm. 18.An assembly for providing tension on a load bearing member in anelevator system, comprising: an elongate tension member having a firstend that is adapted to be secured to one of a cab or a counterweight; adamper that is adapted to be supported for movement with the other ofthe cab or the counterweight, a second end of the tension member beingassociated with the damper such that the damper absorbs a load on thetension member under selected conditions; and a base module that isadapted to be secured in a pit and that includes at least one sheavehaving an axis of rotation that remains stationary relative to the pit,the tension member at least partially wrapping around the sheave. 19.The assembly of claim 18, wherein the damper includes at least one of anair spring, a hydraulic actuator, a pneumatic actuator or a mechanicalspring.